1. Technical Field
The present invention relates to a driving force transmission device and an image forming apparatus using the same.
2. Description of Related Art
An image forming apparatus including a unitized consumable component such as a photoconductor drum has been known. Such a unitized consumable component is removably attached to the main body (hereinafter referred to as an apparatus body) of the image forming apparatus to be exchanged by a user. For example, each of a photoconductor drum, charging device, developing device, and cleaner is unitized to be removed from the apparatus body, and a driving force is transmitted to these units from the apparatus body. A tandem image forming apparatus includes four image forming units corresponding to the four colors of yellow, magenta, cyan, and black. These image forming units are attached to the apparatus body, so that photoconductor drums, development rollers, and the like rotate to form an image. The apparatus body also includes a motor and a speed reduction unit which are driving sources for rotating the photoconductor drum, the development roller, and the like. The speed reduction unit is connected to the photoconductor drum to transmit driving force.
Various connection members between the speed reduction unit and the photoconductor drum have been proposed. For example, a spline coupling using an external gear and an internal gear has been proposed. Since the image forming unit is removably attached to the apparatus body, when the photoconductor drum and the speed reduction unit are connected by this spline coupling, eccentricity and a deflection angle occur between the output shaft of the speed reduction unit provided in the apparatus body and the shaft of the photoconductor drum attached to the speed reduction unit. Such eccentricity and a deflection angle also occur between the shafts of the external gear and the internal gear.
An image forming apparatus described in Patent Literature 1 (Japanese Patent No. 4775947) includes a serration coupling using a guide member. However, since such a serration coupling does not have a configuration which absorbs shift and eccentricity between a driving shaft and a driven shaft, an axis reaction force may occur due to a variation in component accuracy, resulting in deterioration in rotation of a driving target.
An image forming apparatus described in Patent Literature 2 (Japanese Laid-Open Patent Application No. 2007-240007) has a configuration which absorbs such shift and misalignment between a driving shaft and a driven shaft. A parallel pin is pressed into the driving shaft and the driven shaft, and an intermediate body engaging with the parallel pin is held to reduce the axis reaction force due to a variation in component accuracy. However, such a configuration doubles the rotation irregularity since the driving force is transmitted by the two positions of the top and bottom portions of the parallel pin.
Patent Literature 3 (Japanese Laid-Open Patent Application No. 2014-142431) describes a configuration in which crowned teeth of an internal gear and an external gear of an intermediate body engage with an internal gear of a flange and a sintered gear pressed into a drum shaft, respectively, so as to reduce the axis reaction force in the engagement portions. However, in order to hold the intermediate body, an image forming apparatus described in Patent Literature 3 requires an internal gear flange having a member for determining a coaxial level and a member for retaining the intermediate body to be pressed into a drum. Consequently, such an image forming apparatus has a problem in an assembly performance, and may deteriorate highly accurate straightness and deflection that are required for a drum such as a photoconductor drum.
Patent Literatures 3 describe a technique using a two-stage spline joint including a flexible intermediate body having a crowned external gear to improve rotation irregularity by dispersing load with the increased number of driving force transmission portions (teeth number). However, when this configuration is applied to the flange of the drum such as a photoconductor drum, it is difficult to provide the crowned external gear to the drum in view of a layout.